An electronic access control device, or more commonly, an electronic combination lock, does not require a key to open the lock. This eliminates the problems associated with keys such as the cost of producing the keys and the cost of replacing lost keys. Electronic access control devices are known, for example, from U.S. Pat. No. 5,021,776. In this device, and other common electronic access control devices, a microprocessor is used in combination with a keypad and an electrically programmable read only memory (EPROM). The microprocessor compares the combination entered in the keypad by the operator with the combination stored in the EPROM. If the two combinations match, the microprocessor opens the lock.
Problems associated with previous electronic access control devices fall into two areas. The first area concerns the operation of the stand alone unit in terms of manufacture and use. Problems associated with manufacture include difficulty in programming the EPROM. EPROMs, which usually require parallel programming, interrupt the manufacturing process in that they restrict when the manufacturer can program the device. A manufacturer would prefer to program the access code into the EPROM as the last step in the manufacturing process. However, with parallel EPROMs, burning in the code after the device is manufactured is difficult. After the device is soldered together, the manufacturer must contend with integrated circuit pin clips and must worry about interference with other circuitry on the manufactured device. Further, manufacturing, with known electronic access control devices, requires many pin connections which increase manufacturing cost.
Problems associated with use include reliability and ease of use of the electronic access control device. Electronic access control devices, by their nature, must be extremely reliable. However, when the device contains a significant number of pin connections, the reliability of the device decreases. Further, serial access to the EPROM to determine the electronic access code is easier than parallel access in terms of pin connections. When the user forgets or loses the access code in the EPROM, a locksmith could plug into the device and retrieve the access code serially without breaking into the safe. However, with parallel EPROMs, serial access is not available. Moreover, another problem associated with use is the limited power associated with the battery. The use of a solenoid in opening the lock is power intensive. Thus, the battery is limited in its operative life.
The second area of problems associated with electronic access control devices is remote use. The problems focus on the power constraints of electronic locks. Often, one may be interested in powering remote access locks by battery if a constant power source is not available. However, batteries cannot be used since remote units consume a great deal of power in standard operation and therefore are too power intensive to be powered by batteries.